The field of this invention is jars for downhole use in operations such as drilling and fishing and more particularly to fluid operated jars that function bi-directionally.
Jars are downhole devices that are used to impart a blow in an uphole or downhole direction to a stuck object. They have also been designed to impart rotary motion so that a drill bit can be turned as well as hammered during a drilling operation. There are the purely mechanical types that deliver a fixed jarring force triggered by pulling up on the string. There are hydraulic versions that generally have two telescoping members with fluid reservoirs annularly disposed in between. A small orifice through which the oil has to pass resists the initial pulling of the string. This passage is in a movable piston that isolates the two annular cavities as the pulling force is applied. Eventually, the movable piston with the orifice in it clears a narrow passage allowing oil to rush around it and allowing the telescoping members to contact each other to deliver a hammer blow to an anvil.
Yet other designs of jars have used the concept of valves in pistons, which when closed allow pressure buildup to move telescoping members with respect to each other and against the force of a spring. As more relative movement under these conditions occurs, the spring force eventually overcomes the hydraulic force holding the valve in the piston closed and the movement of the telescoping members is violently reversed. This results in a hammer blow delivered to an anvil as the tool reassumed the initial position for a repetition of the same cycle. A good example of this style of bi-directional jar is U.S. Pat. No. 5,803,182. While this design can hammer bi-directionally, it did not have the capability of also delivering rotary motion to a drill bit. Another example of a bi-directional hydraulic jar is U.S. Pat. No. 4,462,471.
Prior attempts to provide bit turning capability to jars involved the provision of a pin extending in a spiral slot to convert axial movement in the jar to a rotational output at the bit secures at its lower end. An example of this design is U.S. Pat. No. 4,958,691. It features the use of a plurality of tilting cams to insure rotation in a single direction for drilling. This tool did not have bi-directional capability and the mechanical reliability of the arrangement of the pin in the spiral slot was less than ideal.
The present invention addresses the limitations of the prior designs and seeks to accomplish a variety of objectives in a single tool, some of which will be enumerated. The jar of the present invention delivers bi-directional jarring capability in conjunction with the ability to impart rotational motion for drilling. The clutching system addresses the reliability issue in a drilling environment. Cushioning members reduce wear on valve seats from cyclical loading. Modularity allows for rapid conversion from bi-directional operation to unidirectional operation. Use of a singular spring system for jarring in opposite direction and other features allow reduction of overall length of the jar, in comparison to existing bi-directional jars. The number of parts is also reduced to aid the objective of reliability and overall length reduction. These and other objectives will be more apparent to a person skilled in this art from a review of the detailed description of the preferred embodiment described below.
Also relevant for background in the field of downhole jars are U.S. Pat. Nos. 4,076,086; 4,361,195; 4,865,125; 5,086,853; 5,174,393; 5,217,070; 4,462,471; 6,062,324; 6,035,954; 6,164,393; and 6,206,101.
A bi-directional jar with bit turning capability is disclosed. To jar down, weight is set down on the tool and pressure is built up on a piston to move the body up while compressing a spring. When spring force opens the valve in the piston, the housing comes down striking an anvil as the flow rushes through the piston before the valve recloses for another cycle. The valve member features a hydraulic brake to slow its movement after the valve is forced open. Clutching action comes from an angled spline acting through a spirally cut cylinder, which reduces in diameter to engage the bit to turn. A single spring acts on a pair of pistons for bi-directional jarring. Modularity allows rapid conversion to uni-directional operation.